Spark-plug insulator



Tatenlteol @cil.3ll, T922.

UNHTED sTaTas PATENT orator.

TAINE Gr. MODOUGAL, 0F ELI GOMPANY, OF FLINT,

No Drawing.

To all whom it may Be it known that a citizen of the United dent of Flint, county of 5 of Michigan,

NT, MIGHIGAN, ASSIGNOR 'IO CHAMPION IGNITION MICHIGAN, A. CORPORATION OF MICHIGAN SPARK-PLUG INSULATOR.

Application filed october 30, 1920. Serial No. 420,680%.

concern.-

I, TAINE G.-MODOUGAL,

States, and a resi- Genesee, and State have invented certain new and useful Improvements in Spark-Plug Insulators, of which the following is a full, clear, concise, and exact description such as will enable others skilled in the art to which the invention relates to make and use the same.

The invention relates to the manufacture of porcelain products and has particular reference to insulators, such which are required to exhibit a sulators,

high degree of dielectric strength ness under as spark plug inand toughconditions such as exist in the internal combustion engine, especially in the presence of pressures as occur,

such extreme temperatures and for example, in aeroplane engines.

In an endeavor to impart these qualities to porcelain articles of the type referred to,

large a content as possible of calcined material, the remainder of made up of the mixture being a blend of various clays. In one of the processes of manufacture commonly employed, it is customary to shape the article from a plastlc mass comprising the said body mixture, to dry the formed article to a condition of leather hardness, to finally shape the partially dried article to desired dimensions by a turning operation or other wise, and then to complete the drying, after which the article may be fired 1n manner.

the usual It has been found dilficult hitherto to form mixtures w hi'ch possess suflicient toughness to withstand the treatment by the process stated, especially leather hardness,

the turning while at a and which exhibit sufficiently high thermo-dielectric strength and toughness when fired. So far as I am aware, no such mixtures have been found desirable or commercially successful in which the content of calcined material, which is in itself nonplastic,

- percentage the remain has amounted to more than ap- 't has been necessary to use for der of the mixture a blend of Even with this clays some of which are of extraordinary plasticity. A number of clays have been known for many years which, owing to their extreme fineness or colloidal nature, are capable of imparting plasticity to relatively large proportions of non-plastic bodies, among which may be mentioned the ball clays, such as English and Kentucky ball clays, bentonite clay and ehrenbergite clay, as well as clays to which have been added small amounts of electrolytes or of certain gums. In the preparation of body mixtures for spark plug porcelains, the ball clays have been generally used, the English clay being particularly valuable. It has been found commercially impracticable, however, to use more than approximately twenty percent of the ball clays, owing to the fact that, when used in larger amounts, they impart undesirable properties to the product, such as air cracking and warping while drying,

"tion to their use on a commercial scale.

The principal object of my invention, therefore, is to produce a spark plug insulator, or like ceramic article, or a composition therefor, in which the content of non-plastic mineral ingredients imparting thermo-dielectric strength and toughness is extraordinarily high, at the same time maintaining the qualities necessary to permit the mixture to be satisfactorily worked into the desired shapes. To this end I propose to utilize a proportion of the plasticity imparting clays much less than ordinarily employed, including therein preferably a small percentage of ball clay and a still smaller percentage of bentonite clay, also employing in the mixture a relatively large proportion of kaolins or china clays, which are more satisfactory than ball clays from the standpoint of their efiect upon the burned product.

The extremely high plasticity ofbentonite clay has been referred to in lications, for example in Clays, by Ries, published in 1906, pp. 457-458, and in an article y varlous pub--;

W. G. Knight in Eng. and Min. Joun,

" or both,

- the properties desirable much as five percent,

' one to three percent.

manufacture of porcelain is suggested in the article by Mr. Knight, but serious difficulties have been found to attend attempts by ceramists to utilize it in ractical application- Ries and Keele anadian Dept. of Mines, Report on the Clay and Shale Deposits of the Western Provinces, 1913, pp. 56 and 74), experimented with mixtures of three parts sand and one part bentonite clay and refer to the plasticity imparting characteristics of the material, but they point out (pp. 74 and 89-90) that the products formed from bentonite clay crack badly in air drying. In fact these experimenters concluded that the presence of bentonite clay is a potent factor in producing air cracks in mixtures containing it, which fact they demonstrated by tests performed upon clay mixtures containing ten percent of bentonite clay (p. 90).

0 far as I am aware, the universal experience hitherto in attempting to usebentonite clay in mixtures has been with similar results, i. e. that air cracking or warping, drying or burning, or both, to such an extent that the use of the material was not commercially practicable. I have found, however, that by suitable combination of proper balancing of the proportions thereof, and the use of relatively very small percentages of bentonite clay, it is possible to prepare body mixtures which not only are free from the defects previously deemed inseparable from the use of this material, but which possess, to an enhanced extent, for ceramic articles of the type herein mentioned.

he percentage of bentonite clay which is necessary in order to enable a satisfactory mixture to be produced without causing air. cracks or warping will, of course, vary somewhat-with the proportions of the other ingredients making up the plastic content, but in no case does it amount to as in fact the most satisfactory results have followed the use of from small percentage, however, renders possible a material increasein the non-plastic conduced, thus enabling the product to be improved by either, or both, reducing the content of ball clay or increasing that of. 6.1-

CIIIGS,

Calcines ingredients and The addition of this percentage. would have To make the effect clearer, I refer to the following diagrammatic representation of the possible manlpula-tion of proportions. Ca10mes H M: China clay I Ball clay China i Calcmes clay Bal1 clay 60% 10% 30% Ben- Ball tonclay i'te m E: 60% 30% 7% 3% The first line of the table indicates a typical mixture as hitherto constituted, approx imately twenty percent of ball clays being necessary in order to enable the use of fifty percent of calcines.

' The second line indicates the approximate change which is necessary with the use of ball clays in order to increase the content of callcines to sixty percent, i. e. the amount of ba 1 rendering the mixture commercially quite impracticable. I

The third line indicates a mixture in which, by the use of bentonite clay, the prohas been raised and that of ball clays lowered, without necessitating a reduction in the original content-of china clays.- These ingredients in substantially the proportions indicated, viz.

Non-plastic material (mostly or all China clay calcines) 60% China clays (which may comprise a mixture of Florida and English kaolin) 30% Ball clay (for example Kentucky.

ball) 7% Bentonite clay 3% constitute a practical body mixture applicable to the manufacture of porcelain insulators for spark plugs. The non-plastic materials will comprise preferably ingredients such as magnesite, calcium carbonate, flint, aluminum oxide, and china clay, which may be mixed, heated or calcined, and subsequently ground to a fineness such as to pass througha screen of 120 mesh. The particular proportions or ingredients making up whatever percentage of non-plastic content may be decided upon, may be varled widely as desired to determine the properties of the burned product without, however, requiring variation 'in the proportions of the plastic ingredients or affecting the working qualities of the composlte mass. A reduction of the relative amount of nonplastic content may be accompanied by a corresponding reduction in the percentage of bentonite clay or ball clay, or both.

The articles formed from a porcelain body mixture ofthe type marked advantages over those hitherto obtainable by the method above set forth as clays must also be increased, thereby indicated possess cient toughness maaaae commercially employed. The materially higher content of non-plastic ingredients imparts to the product higher thermo-dielectric strength and greater mechanical toughness, while the reduction in the proportion of ball clays in the plastic content results in an improvement in the color and also in the mechanical toughness of the product.

I claim:

1. A porcelain body mixture comprising a non-plastic mineral content of not less than approximately sixty percent, the remainder comprising a arting plasticity to the mixture and suflito permit Working when dried to leather hardness but without producin air cracks in drying.

2. i5 porcelain body mixture comprising a non-plastic mineral content of over percent, the remainder consisting of clays including china cla ball clay, and bentonite clay, the latter to the amount of less than five percent of the entire mixture.

porcelain body mixture comprising a relatively large non-plastic mineral conblend of clays imtent adapted to impart thermo-dielectric strength and toughness to the burned product, and a plastic content of clays including china clay, ball clay, and bentonite clay, the latter to the amount of not more than three percent of the entire mixture.

4:. A ceramic composition for spark plug insulators comprising a non-plastic content of approximately sixty percent and a plastic content including approximately thirty percent of china 0 ay', seven percent of bal clay, and three percent of bentonite clay.

5. A spark plug insulator body comprising, before being fired, over fifty percent of non-plastic mineral material adapted to impart. thermo-dielectric strength and toughness to the 'burned product, and a plastic content comprising china clay, ball .clay and bentonite clay, the body being suiiiciently tough to permit shaping when dried to leather hardness.

6. A refractory material containing not more than 5% of bentonite.

In testimony whereof I ailix my signature.

- TMNE @r. MGDOUGAL 

